1. Field of the Invention
This invention relates to the processing of electronic components and, more particularly, to methods and apparatus for solder tinning component leads.
2. Description of the Prior Art
The utilization of electronic components in a wide variety of devices has continually increased from year to year. The electronic components usually have suitable lead wires attached thereto to enable the component to be mounted on printed circuit boards, for example, the lead wires being soldered to appropriate points on the opposite side of the printed circuit board. When the desired number of electronic components have been inserted in the printed circuit board and the soldered connections have been made, the assembly so formed is then ready for incorporation in the device being manufactured.
In general, manufactured electronic components, such as axial lead resistors, are pre-packaged in a reel with opposite component leads being secured by tape. These reels are then sold to distributors or manufacturers for incorporation into electrical devices being manufactured. Situations arise, however, wherein the reel itself or the components on the reel are not utilized for extended periods of time. In this case, depending on the type of coating on the component leads, the leads may be quite unsuitable for making reliable electrical connections when the components are installed in electrical circuits, as in printed circuit boards and the like. For example, the leads of electrical components, as manufactured today, are frequently coated with a plated layer which does not have a long shelf life insofar as solderability in the making of circuit connections is concerned. Modern fabrication techniques often deposit this layer by electroless nickel plating or by electrolytic tin or nickel plating. Rather than being a continuous layer, the result is likely to be a surface of discontinuous microscopic balls or globules which, if solderable upon fabrication, become degraded within a short time to the point where satisfactory solder connections cannot be reliably and consistently formed. In such cases the shelf life is relatively short; typically within six months a large proportion of such leads are unsolderable because of the development of oxidation and other inhibiting properties.
There are other instances of fabricated electronic components intended for ultimate use by installation in electrical circuits by means of soldered connections where it is necessary to remove an outer incompatible layer before the leads can be soldered. An example of such is a gold plating layer formed over a base lead of brass or copper, such as occurs in certain components which include a plated layer of gold as a constituent element of the component and wherein the gold plating is continued externally of the component onto the base metal lead. While gold is a solderable material, it may tend to embrittle the solder joint, particularly where the gold layer exceeds a certain thickness. Thus certain Mil-Specs require that a gold plated layer be removed in preparing component leads for solder connections. While this can be accomplished by immersing the lead in a solder bath which at the same time solder-tins the base lead, the process of treating each component lead in this fashion on an individual basis can be quite laborious and costly.
Conventional techniques for solder tinning component leads have been almost, if not entirely, discontinuous in nature and involve relatively delicate, tedious and time-consuming hand operations of limited production which contribute materially to the cost of the finished product. In particular, handling each component to pre-clean, flux, solder, post-clean and re-package the components necessitates a considerable amount of labor. However, certain Mil-Specs require that the electrical connection to a component lead be completed by soldering to develop a fused coating. Thus it has been necessary heretofore, when fabricating electronic circuitry to these Mil-Specs, to prepare the component leads in this fashion.
U.S. Pat. No. 2,954,117 provides a technique for manufacturing a wafer-type capacitor using mass production techniques and in particular calls for at least one terminal of the electrical circuit component being securely fastened to a carrier member until the time it may be desired to remove the circuit component for permanent assembly in a selected electrical device. The carrier member moves the terminal leads through various fabricating steps or stations as the capacitor is being manufactured. Although the process disclosed in this patent provides an automated technique for fabricating electrical circuit components such as capacitors, the special requirements for solder tinning a component lead to preserve the solderability and to prolong the shelf life of a component lead and, in particular, the necessary step of removing tape from both sides of the terminal lead to allow solder tinning thereof and the re-application of the tape after the processing has been completed is not disclosed.
U.S. Pat. No. 3,394,441 also discloses a method of manufacturing capacitors wherein a web conveyor is provided to continuously position, transfer, introduce and remove capacitor constituent elements and progressively form sub-assemblies thereof relative to a plurality of sequentially arranged, cyclically operable and adjacently positioned operating stations. The sequential fabricating steps are concurrently and sequentially effected on the conveyor strip supported work pieces. Included in the process is a terminal wire sub-assembly forming an insertion station C wherein a length of terminal wire is formed and inserted into the terminal wire sub-assembly mounting slits in the web. As discussed hereinabove with respect to U.S. Pat. No. 2,954,117. U.S. Pat. No. 3,394,441 is solely concerned with the manufacturing of components and does not address the problem of solder tinning a component lead to preserve the solderability and to prolong the shelf life thereof.
U.S. Pat. No. 3,995,588 describes a technique for coating the axially extending leads of a sealed contact with solder to protect them from contamination and to enhance their solderability into circuits. The sealed contact is transported along various processing stations in the apparatus disclosed. However, as with the aforementioned patents, U.S. Pat. No. 3,995,588 does not address the problem of removing tape from component lead already solder tinned to allow the subsequent tinning of the leads.
U.S. Pat. No. 2,929,130 discloses a process for mass producing small electronic components such as resistors or capacitors. The electronic components pass through a series of consecutive stages, the objects being attached individually to a strip of flexible material which is led through the stages of manufacture and which is driven so as to convey the objects, one after the other, through the stages. A suitable material for the strips as disclosed is paper. As set forth hereinabove with respect to the aforementioned patents, U.S. Pat. No. 2,929,130 does not disclose a technique for removing standard tape attached to each end of the axial lead component to tin the component leads.
What is therefore desired is a technique which operates in conjunction with a plurality of electronic components which have been secured together by tape in a manner such that the tape covering at least one of the leads of each component is removed and such that the component lead can then be solder tinned to preserve the solderability of the lead and also to prolong its shelf life.